Although Israel's political system does not specify that the party with the most votes is guaranteed to form the next coalition, Mr Netanyahu is widely expected to be handed the task of pulling together 61 MPs to form a majority.

But the Knesset may now be nearly split between right and left blocs, which will make choosing a governing coalition difficult.

It could mean Israelis will be heading back to the polls early if a fragile government cannot hold together.

Mr Netanyahu says he intends to form as broad a governing coalition as possible, suggesting he would go beyond a traditional alliance with other right-wing and religious partners.

"The first challenge was and remains preventing Iran from obtaining nuclear weapons," he said.

Mr Netanyahu has called Tehran's nuclear program an existential threat to Israel and has stoked international concern by hinted strongly at possible Israeli military action to stop Iran from developing an atomic bomb.

Final election results, which must include votes cast by Israeli troops, are not due out for another week.